The fundamental objectives of the proposed program are to gain an understanding of the mechanisms by which cellular functions are regulated by protein phosphorylation, and to elaborate on the role of protein phosphorylation as the mechanism of action of cAMP. In each area the control of glycogen metabolism will serve as a model system. We propose an investigation of the phosphorylation of phosphorylase kinase and glycogen synthetase in the perfused rat heart so that we may identify and distinguish control processes mediated by cAMP and those otherwise regulated. That investigation is necessarily coordinated with the purification and physicochemical characterization of cardiac phosphorylase kinase and glycogen synthetase. We shall try to determine the specific functions of the subunits of phosphorylase kinase. We propose to compare and contrast the mechanism of action of cAMP in regulating the functions of a differentiated myocyte with the role of the cyclic nucleotide in modulating proliferation of these cells. We will use either skeletal or cardiac cells in culture for these experiments and the regulation of glycogen metabolism will serve as the primary model of a cAMP-mediated event of the differentiated cell. Our study of glycogen metabolism in cultured cells will be expanded to an understanding of the process(es) that may regulate synthesis of the key enzymes; in particular the coordination of synthesis of the subunits of phosphorylase kinase. In both the perfused heart system and the cultured muscle cells we will probe key features of dibutyryl cAMP metabolism and mechanism of action and of cAMP-dependent protein kinase activation.